The present invention relates to a device for the detection of a high voltage. The device can be applied especially to integrated circuits comprising electrically programmable non-volatile memory elements.
The programming of non-volatile memory elements requires the use of a high voltage. For example, for an integrated circuit supplied at 2.5 volts, this high voltage reaches about 8 volts. In certain circuits, this high voltage is generated internally using a charge pump.
In other circuits, this high voltage is applied to an external pin of the integrated circuit. In this case, the customer specification for the integrated circuit gives indications on the required characteristics of this voltage. These characteristics include a nominal value, a range of values around the nominal value, and a timing window of application of this high voltage before internal use. For example, the client specification may indicate that the high voltage has a nominal value of 8 volts in a range of 7.5 to 9 volts, and must be applied in a timing window of 500 nanoseconds to 1 millisecond before it is effectively used internally. The user seeking, for example, write access to a memory element must follow a certain timing sequence to send a write command with the address and the data to be written, and to apply the high voltage.
With respect to the integrated circuit, there is a timing window for the external application of the high voltage. It is known that the high voltage is applied during this window but the instant at which it is applied is not known. Furthermore, the slope at which this high voltage is applied is not known. If the voltage build-up slope is very steep, the high voltage is applied with excessive suddenness to the MOS transistors of the circuit. This may cause the transistors to breakdown. If it is too slow, there is a risk that the high voltage will be used outside the specified value range. This may lead to a loss of information, i.e., a wrong writing.
In view of the foregoing background, it is an object of the present invention to detect the application of a high voltage to an integrated circuit to enable use of this high voltage in a manner that is optimal for the integrated circuit. An optimal use of the integrated circuit may particularly include the regeneration of an adapted high-voltage ramp, or the control of the application of this high voltage to circuits with an optimal value.
The invention can equally be applied to the case where the high voltage is generated internally. The detection of the application on an internal node enables the generation of the sequencing signals as a function of the effective level attained by the high voltage. This makes it possible to carry out the independent sequencing of parameters affecting the operation of the charge pump.
Another object of the present invention is to detect the presence of the high voltage so as to put the reference voltage generators into operation, thus enabling a reduction in the stress on the MOS transistors.
These and other objects, features and advantages in accordance with the present invention are provided by a high voltage detection device capable of detecting the crossing of a threshold on a signal given by a high-voltage divider comprising a voltage detection circuit connected between the logic supply voltage and ground. The device further comprises a negative feedback loop to limit the voltage at the output of the divider after the crossing of the threshold. The detection circuit operates in a range of logic voltage levels, thus enabling the use of standard transistors.
The invention therefore relates to a device for detecting the application of a high voltage to an internal node of an integrated circuit. The device comprises a high-voltage divider circuit and a threshold detection circuit receiving a signal at an input given by the output node of the divider circuit, and providing a threshold crossing detection signal at an output of the threshold detection circuit.
The detection circuit is preferably a circuit connected between the logic supply voltage and ground. The detection device furthermore comprises a negative feedback loop at an output of the divider circuit to limit the voltage build-up at the output node of the divider circuit after the crossing of the detection threshold.